Scanning exposure apparatus

ABSTRACT

A scanning exposure apparatus which promptly analyzes a cause for a variation in exposure line width. The scanning exposure apparatus includes a mask stage on which a mask is placed, a wafer stage on which a wafer is placed, a focusing mechanism which detects surface position information of the wafer and adjustment means which adjusts the surface position of the wafer. Control means acquires pose information of the wafer adjusted by the adjustment means at the time of exposure and stores the pose information in a memory in association with preacquired surface shape information of an exposure area. A state in which the exposed surface of the wafer has been exposed with respect to exposure light is known from the pose information and the surface shape information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of pending U.S.patent application Ser. No. 09/817,316 filed on Mar. 26, 2001, nowabandoned entitled “Scanning Exposure Apparatus”.

BACKGROUND OF THE INVENTION

The present invention relates to a scanning exposure apparatus, and,more particularly, to a scanning exposure apparatus which is used in thelithography process for fabricating micro devices, such as asemiconductor device, liquid crystal display device, image pickup device(CCD or the like) and thin-film magnetic head.

One known scanning exposure apparatus of this type comprises a maskstage on which a photomask or reticle (hereinafter called “mask”) havinga circuit pattern formed thereon is to be placed, a substrate stage onwhich a substrate (wafer, glass plate or the like) coated with aphotosensitive material is to be placed, a focusing mechanism whichdetects surface position information of the substrate and adjustmentmeans which adjusts the surface position of the substrate based on theresult of detection by the focusing mechanism. This scanning exposureapparatus moves individual shot areas of a wafer into the exposure fieldof a projection optical system one after another and sequentiallyexposes the pattern image of a mask on the individual shot areas.

For example Japanese Unexamined Patent Publication No. 06-283403discloses a known surface position setting apparatus (focusingmechanism) for use in such a scanning exposure apparatus. The surfaceposition setting apparatus is provided with multi-point measuring meansthat measures the height of a substrate parallel to the optical axis ofthe projection optical system at a plurality of measuring points of thesubstrate in the scanning direction and a direction intersecting thescanning direction. At the time of scanning the substrate, the surfaceposition setting apparatus measures the height at each measuring pointwith respect to an exposure field which is conjugate with anillumination area of a predetermined shape with respect to theprojection optical system when the substrate is scanned. Based on themaximum and minimum values of the results of measuring the individualmeasuring points, the surface position setting apparatus acquires theaverage surface of the exposure surface and then acquires a differencebetween the height of the average surface and the height of the imagesurface of the projection optical system. Next, the surface positionsetting apparatus sets the height of the substrate with the substratestage based on the difference and aligns the exposure surface.

When the exposure line widths of patterns formed on the individual shotareas of the substrate vary, the conventional scanning exposureapparatus cannot quickly find out the cause or reason for the occurrenceof the variation and requires a considerable time and a significantamount of labor to analyze and check the cause.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide ascanning exposure apparatus which quickly analyzes a cause of avariation in exposure line width.

According to the first aspect of the present invention, there isprovided a scanning exposure apparatus for projecting an image of apattern of a mask on a substrate using exposure light and relativelyscanning the substrate with the exposure light, thereby exposing anexposure area on the substrate. The scanning exposure apparatus includessurface position detection means for detecting surface positioninformation of the substrate, and adjustment means for adjusting asurface position of the substrate based on the result of detection bythe surface position detection means. The scanning exposure apparatusfurther includes control means for acquiring pose information of thesubstrate adjusted by the adjustment means at the time of exposure basedon a detection signal from the surface position detection means andstoring the pose information in a memory in association with preacquiredsurface shape information of the exposure area on the substrate.

According to the second aspect of the present invention, there isprovided a scanning exposure method of projecting an image of a maskpattern on a substrate using exposure light and relatively scanning thesubstrate with the exposure light, thereby exposing an exposure area onthe substrate. The scanning exposure method includes the step ofdetecting pose information of the substrate by detecting a surfaceposition of the substrate at the time of exposure, and the step ofpredicting a state of the image of the pattern to be formed on thesubstrate based on the detected pose information and preacquired surfaceshape information in an exposure area of the substrate.

According to the third aspect of the present invention, there isprovided a management apparatus which manages exposure processinformation of a scanning exposure apparatus. The exposure apparatusincludes surface position detection means for detecting surface positioninformation of a substrate and adjustment means for adjusting a surfaceposition of the substrate based on the result of detection by thesurface position detection means. The scanning exposure apparatusprojects an image of a pattern of a mask on the substrate using exposurelight and scans relatively the substrate with the exposure light,thereby exposing an exposure area on the substrate. The managementapparatus includes an interface connected to the scanning exposureapparatus, and control means for acquiring pose information of thesubstrate adjusted by the adjustment means at a time of exposure basedon a detection signal from the surface position detection means acquiredvia the interface, and storing the pose information in a memory inassociation with preacquired surface shape information of the exposurearea on the substrate.

According to the fourth aspect of the invention, there is provided amanagement method which manages exposure process information of ascanning exposure apparatus. The scanning exposure apparatus includessurface position detection means for detecting surface positioninformation of a substrate and adjustment means for adjusting a surfaceposition of the substrate based on the result of detection by thesurface position detection means. The scanning exposure apparatusprojects an image of a pattern of a mask on the substrate using exposurelight and scans relatively the substrate with the exposure light,thereby exposing an exposure area on the substrate. The managementmethod includes the step of acquiring a detection signal from thesurface position detection means via an interface from the scanningexposure apparatus, the step of acquiring pose information of thesubstrate adjusted by the adjustment means at the time of exposure, andthe step of predicting a state of the image of the pattern to be formedon the substrate based on the pose information and preacquired surfaceshape information of the exposure area on the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention that are believed to be novel areset forth with particularity in the appended claims. The invention,together with objects and advantages thereof, may best be understood byreference to the following description of the presently preferredembodiments together with the accompanying drawings.

FIG. 1 is a structural diagram of a scanning exposure apparatusaccording to the first embodiment of the present invention, mainlyillustrating a focusing mechanism thereof;

FIG. 2A is an explanatory diagram showing the relationship betweenmultiple measuring points on an exposure surface and an exposure field;

FIG. 2B is an explanatory diagram showing the layout of opening patternson a pattern forming plate;

FIG. 2C is an explanatory diagram showing the layout of photosensor on aphoto-detector;

FIG. 3 is a structural diagram of the scanning exposure apparatus ofFIG. 1, mainly illustrating a mask stage and substrate stage thereof;

FIG. 4 is a plan view showing a plurality of shot areas on a wafer;

FIG. 5 is a structural diagram illustrating an auto-focus andauto-leveling mechanisms in the scanning exposure apparatus of FIG. 1and a control structure therefor;

FIG. 6 is a schematic diagram depicting a ΔCD management apparatusconnected to the scanning exposure apparatus;

FIG. 7 is a block diagram showing the ΔCD management apparatus;

FIG. 8 is a flowchart illustrating a ΔCD measuring process sequence;

FIG. 9 is a graph showing CD defocus data;

FIG. 10A is an explanatory diagram showing flatness data in a singlemeasuring shot area;

FIG. 10B is an explanatory diagram showing the relationship between anexposure field and an exposure surface at the time of exposure;

FIG. 10C is an explanatory diagram showing a variation of one point withrespect to an image forming surface;

FIG. 11 is an explanatory diagram showing the relationship between aslit exposure field and an exposure surface at the time of exposure;

FIG. 12 is a graph showing a device topography of a single shot area;

FIG. 13 is a graph showing a Z average offset of a single shot area;

FIG. 14 is a graph showing a movement standard deviation of a singleshot area;

FIG. 15 is a graph showing target values of individual portions in asingle shot area at the time of exposure;

FIG. 16 is a graph showing trace errors of individual portions in asingle shot area at the time of exposure;

FIG. 17A is a graph two-dimensionally showing a variation amount ΔCD ofexposure line widths of individual portions in a single shot area;

FIG. 17B is a graph showing the variation amount ΔCD in the form ofcontour lines;

FIG. 18 is a graph showing the relationship among a Z average offset, amovement standard deviation (CDP Amplitude) and an exposure line width;

FIGS. 19(A)-19(C) are diagrams showing wedge mark CD magnificationtechnique using double exposure;

FIGS. 20(A), 20(B) and 20(D) are graphs showing X-Y sync errorsintroduced to a calculation of the CD variation;

FIG. 20(C) is a graph showing sync-error distribution;

FIG. 21 is a flowchart illustrating a CD variation map generatingprocess sequence;

FIG. 22 is a structural diagram of a scanning exposure apparatusaccording to the second embodiment of the present invention;

FIG. 23 is a block diagram showing a ΔCD management apparatusincorporated in the main control system of the scanning exposureapparatus shown in FIG. 19; and

FIG. 24 is a flowchart exemplifying a device manufacturing process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of a scanning exposure apparatus according to thepresent invention will be described below referring to FIGS. 1 through19.

As shown in FIGS. 1 and 3, a scanning exposure apparatus 21 includes anillumination optical system 22, a mask stage 23 on which a mask M havinga predetermined pattern formed thereon is placed, a projection opticalsystem 24 and a wafer stage 25 as a substrate stage on which a wafer Was a photosensitive substrate is placed. The scanning exposure apparatus21 further includes a focusing mechanism 26 of an off-axis type thatconstitutes a part of surface position detection means which detectssurface position information of the wafer W, and a main control system27 that constitutes a part of adjustment means which adjusts the surfaceposition of the wafer W based on the result of detection by the focusingmechanism 26.

The scanning exposure apparatus 21 projects the pattern of the mask M onthe wafer W using exposure light EL and sequentially exposes exposureareas (a plurality of shot areas SAij shown in FIG. 4) on the wafer W byrelatively scanning the wafer W with the exposure light EL. The scanningexposure apparatus 21 also includes a ΔCD management apparatus 28 (seeFIGS. 1 and 6) as control means which measures the actual state wherethe exposure areas on the wafer W have been exposed and performsanalysis, such as prediction of a variation amount ΔCD of the exposureline width, from the measuring result.

The exposure light EL from a light source 30, such as a high-pressuremercury lamp, a KrF excimer laser, an ArF excimer laser, an F₂ excimerlaser, a metal vapor laser or a YAG laser which generates harmonicwaves, enters the illumination optical system 22. The illuminationoptical system 22 includes various lens systems, such as a relay lens,fly-eye lens (or rod integrator) and condenser lens, an aperture stopand a blind located at a position conjugate to the pattern surface ofthe mask M. When the exposure light EL passes the illumination opticalsystem 22, it is so adjusted as to evenly illuminate a circuit patternon the mask M. The illumination area of the exposure light EL is formedlike slits as indicated by solid lines in FIG. 2A.

As the mask M and wafer W are scanned synchronously with respect to theslit exposure field 76, the circuit pattern on the mask M issequentially exposed on the shot areas SA on the exposure surface Wf ofthe wafer W shown in FIG. 4. For example, the wafer W is scanned in theY direction to the exposure field 76 in the shot area SA11, and isscanned in the −Y direction to the exposure field 76 in the next shotarea SA12. This scanning is repeated thereafter to expose the remainingindividual shot areas one after another, starting with the shot areaSA13.

The mask stage 23 is located under the illumination optical system 22such that its mask mounting surface intersects the optical-axialdirection of the projection optical system 24 at right angles. The maskstage 23 has a Y-directional-mask-drive stage 33 which can be driven ona mask support 32 in the Y direction (perpendicular to the surface ofthe sheet of FIG. 1). A slight-mask-drive stage 34 which forms the maskmounting surface is placed on the Y-directional-mask-drive stage 33. Themask M is held on the slight-mask-drive stage 34 by vacuum chuck or thelike.

The slight-mask-drive stage 34 controls the position of the mask Mslightly and precisely in the X direction parallel to the surface of thesheet of FIG. 1, the Y direction perpendicular to the surface of thesheet of FIG. 1 and the rotational direction (the direction of θ) aroundthe axis parallel to the optical axis of the projection optical system24, within the plane perpendicular to the optical axis of the projectionoptical system 24. A movable mirror 35 (see FIG. 3) is placed on theslight-mask-drive stage 34, and an interferometer 36 on the mask support32 The interferometer 36 always monitors the positions of theslight-mask-drive stage 34 in the X direction, the Y direction and the θdirection. Positional information S1 acquired by the interferometer 36is supplied to the main control system 27.

The projection optical system 24 includes a plurality of lenses whichare unillustrated. When the exposure light EL passes the projectionoptical system 24, its cross-sectional shape is reduced to apredetermined reduction ratio of 1/n (n: a positive integer) from thesize of the illumination area. The circuit pattern on the mask M isprojected and transferred in the predetermined reduction ratio on theexposure surface Wf of the wafer W held on the wafer stage 25 so as tointersect the optical axis of the projection optical system 24.

The wafer stage 25 is located under the projection optical system 24such that its wafer mounting surface intersects the optical-axialdirection of the projection optical system 24. AY-directional-wafer-drive stage 40 which can be driven in the Ydirection is placed on a wafer support 39 of the wafer stage 25. AnX-directional-wafer-drive stage 41 which can be driven in the Xdirection is placed on the Y-directional-wafer-drive stage 40. Providedon the X-directional-wafer-drive stage 41 is a Z-leveling stage 42 whosetop surface can be tilted slightly to the XY plane perpendicular to theoptical axis of the projection optical system 24 and which can be drivenslightly in the Z direction parallel to that optical axis. The wafer Wis held on the Z-leveling stage 42 by vacuum chuck. A movable mirror 43having an L-shaped plane extending in the X direction and Y direction isfixed on the Z-leveling stage 42. A pair of interferometers 44 are soarranged as to face the outer faces of the movable mirror 43. Oneinterferometer 44 shown in FIG. 1 monitors the X-directional position ofthe Z-leveling stage 42, and the other interferometer 44 shown in FIG. 3monitors the Y-directional position of the stage 42. Bothinterferometers 44 monitor the position of the stage 42 in the θdirection. Positional information S2 acquired by those interferometers44 is supplied to the main control system 27.

At the time of exposure, the mask M is scanned in the Y direction to theslit exposure field 76, i.e., in the direction toward or away from thesurface of the sheet of FIG. 1, at a constant velocity V. In synchronismwith the movement of the mask M, the wafer W is scanned in the directionaway from or toward the surface of the sheet of FIG. 1, at a constantvelocity V/β (1/β is the reduction ratio of the projection opticalsystem 24). The synchronous scanning of the mask M and the wafer W iscarried out under the control of the main control system 27.

As shown in FIGS. 1 and 2, illumination light, different from theexposure light EL, which does not expose a photoresist on the wafer W isled to the focusing mechanism 26 from an unillustrated illuminationlight source via a bundle of optical fibers (hereinafter called “opticalbundle fiber”) 47. The illumination light emitted from the optical fiberbundle 47 passes through a condenser lens 48 and illuminates a patternforming plate 49 having multiple slit openings 49-ij (i=1 to 5, j=1 to9; see FIG. 2B). As shown in FIG. 2B, nine slit openings 49-11 to 49-19are formed in the first row on the pattern forming plate 49, and nineslit openings are likewise formed in each of the second to fifth rows.That is, a total of 45 slit openings are formed in the pattern formingplate 49.

The illumination light that has passed the pattern forming plate 49 isprojected on the exposure surface Wf of the wafer W via a lens 50, amirror 51 and an illumination objective lens 52. A pattern image whichis comprised of the slit openings 49-11 to 49-59 of the pattern formingplate 49 is projected on the exposure surface Wf obliquely to the X axisand Y axis, shown in FIG. 2A.

The images of the slit openings 49-ij are projected on the exposuresurface Wf in association with a first row of nine measuring points AF11to AF19 aligned in the X direction above the slit exposure field 76,second to fourth rows of measuring points AF21 to AF49 aligned in the Xdirection within the exposure field 76 and a fifth row of measuringpoints AF51 to AF59 aligned in the X direction below the slit exposurefield 76 in FIG. 2A. In this embodiment, the first row of measuringpoints AF11-AF19 are located at a position apart upward by apredetermined distance (e.g., 4 mm) from one of the long sides of therectangular exposure field 76, and the second row of measuring pointsAF51-AF59 are located at a position apart downward by a predetermineddistance from the other long side of the exposure field 76.

The illumination light that has been reflected at the exposure surfaceWf of the wafer W is projected again on the light-receiving surface of aphoto-detector 56 via a condenser objective lens 53, arotational-direction vibration plate 54 and an image forming lens 55. Inother words, a pattern image comprised of the slit openings 49-ij on thepattern forming plate 49 is formed again on that light-receivingsurface. Multiple photosensors 56-ij (i=1 to 5, j=1 to 9; see FIG. 2C)are laid out on the light-receiving surface of the photo-detector 56.That is, nine photosensors 56-11 to 56-19 are arranged in the first rowon the photo-detector 56 and photosensors 56-21 to 56-59 are likewisearranged on the photo-detector 56, nine in each of the second to fifthrows. A total of 45 photosensors 56-ij (i=1 to 5, j=1 to 9) are laid outon the photo-detector 56 and unillustrated slit apertures are arrangedon the respective photosensors. 56-ij. The images of the slit openings49-ij projected on the respective measuring points AFij (i=1 to 5, j=1to 9) in FIG. 2A are formed again on the associated photosensors 56-ij.

At the time the images of the slit openings 49-ij that have beenreflected at the exposure surface Wf are formed again on thephoto-detector 56, the rotational-direction vibration plate 54 shown inFIG. 1 is rotationally vibrated so as to vibrate the positions of theindividual images in the direction of the short sides of the openings ofthe unillustrated slit apertures. Detection signals detected by thephotosensors 56-ij are supplied to a signal processor 58. The signalprocessor 58 synchronously detects the individual detection signals witha signal of a rotational vibration frequency, thereby generating ninefocus signals corresponding to focus positions in the Z directionparallel to the optical axis of the projection optical system 24 atarbitrary plural points (nine points in the embodiment) in the measuringpoints AFij on the wafer W.

The signal processor 58 normally outputs the nine generated focussignals. The main control system 27 computes the control target positionof the wafer W in the Z direction using an unillustrated internalcomputing section based on the nine focus signals output from the signalprocessor 58. The target position includes control target values for theinclination angles of the exposure surface Wf of the wafer W (the rollor the inclination θx in the X direction and the pitch or inclination θyin the Y direction) and a control target value for an average focusposition (the position of the aligning plane). The main control system27 drives the Z-leveling stage 42 via drive sections 84 to 86 andfulcrums 78 to 80 shown in FIG. 5 based on control signals correspondingto the control target values for the computed inclination angles andposition of the aligning plane. This driving ensures the adjustment ofthe inclination (roll and pitch) of the exposure surface Wf of the waferW and the height thereof in the Z direction so that the exposure surfaceWf is aligned with the aligning plane.

Specifically, when the wafer W is scanned in the Y direction in FIG. 2with respect to the exposure field 76, the main control system 27pre-reads an area located immediately in front of the exposure field 76on the exposure surface Wf by means of three sensors 56-11, 56-15 and56-19 (corresponding to the measuring points AF11, AF15 and AF19) in thefirst row of nine photosensors 56-11 to 56-19 and six sensors 56-21,56-25, 56-29, 56-31, 56-35 and 56-39 (corresponding to the measuringpoints AF21, AF25, AF29, AF31, AF35 and AF39) in the exposure field 76.That is, the Z-directional positions at the nine measuring points AF11,AF15, AF19, AF21, AF25, AF29, AF31, AF35 and AF39 lying in an area 76′located before the exposure field 76 by 4 mm in the scanning directionare pre-read, Likewise, when the wafer W is scanned in the −Y directionin FIG. 2 with respect to the exposure field 76, an area locatedimmediately in front of the exposure field 76 on the exposure surface Wfis pre-read by nine sensors 56-51, 56-55, 56-59, 56-41, 56-45, 56-49,56-31, 56-35 and 56-39. For example, the Z-directional positions at thenine measuring points AF51, AF55, AF59, AF41, AF45, AF49, AF31, AF35 andAF39 lying in an area located before the exposure field 76 by 4 mm inthe scanning direction are pre-read. In this sense, the photosensors56-11, 56-15, 56-19, 56-21, 56-25, 56-29, 56-31, 56-35 and 56-39 arecalled a Y-directional pre-read sensor L1 and the photosensors 56-51,56-55, 56-59, 56-41, 56-45, 56-49, 56-31, 56-35 and 56-39 are called a−Y-directional pre-read sensor L5. The pre-reading is accomplished bysampling nine focus signals, which are normally output from the signalprocessor 58 in association with the nine detection signals from thepre-read sensor L1 or L5, multiple times at a predetermined timing inthe scanning direction by means of the main control system 27 at thetime the individual shot areas are scanned with respect to the exposurefield 76.

Further, the aligning position and the X- and Y-directions inclinationangles of the exposure surface Wf of the wafer W on the Z-leveling stage42 are set to desired values by adjusting the stretching/contractionamounts of the fulcrums 78-80 by means of the drive sections 84-86 (seeFIG. 5) under the control of the main control system 27.

As apparent from the above, the main control system 27 calculates thecontrol target position of the pre-read area of the exposure surface Wfat the time of exposure based on the nine focus signals output from thesignal processor 58 when the pre-read sensor L1 or L5 performspre-reading. The control target position includes the average focusposition of the exposure surface Wf (tho position of the aligning plane)that coincides with the Z-directional position of the image surface ofthe projection optical system 24 and the inclination angles θx and θy ofthe exposure surface Wf at which the image surface and the exposuresurface Wf become parallel to each other. At time t1 which is apredetermined time (the time needed for the wafer W to move 4 mm in thisscanning direction in this embodiment) passed from t0 at which anarbitrary point on the exposure surface Wf is pre-read, the main controlsystem 27 considers that the pre-read area has reached the exposureposition (the lower position of the exposure field 76) and controls theZ-leveling stage 42 so as to align the exposure surface Wf with theimage surface of the projection optical system 24.

As shown in FIG. 3, a reference marker plate 61 is secured in thevicinity of the wafer W on the Z-leveling stage 42 and various referencemarkers are formed on the substrate marker plate 61. Provided above themask M are a pair of mask alignment microscopes 62 for simultaneouslyobserving the reference markers on the reference marker plate 61 and amarker on the mask M. A pair of deflection mirrors 63 are disposedmovable between the mask stage 23 and the mask alignment microscopes 62to guide the detected light from the mask M to the mask alignmentmicroscopes 62. When the exposure sequence is initiated, the deflectionmirrors 63 are moved away sideward from the positions above the mask Mby a mirror driving unit 64 in response to an instruction from the maincontrol system 27. This can associate the wafer coordinate systemdefined by the coordinates that are measured by the pair ofinterferometers 44 on the wafer side with the mask coordinate systemdefined by the coordinates that are measured by the interferometer 36 onthe mask side, or can align the wafer W with the mask M.

As apparent from the above, the main control system 27 controls thegeneral operation of the scanning exposure apparatus 21, including theoperation of positioning the stages 40-42 of the wafer stage 25 and thestages 33 and 34 of the mask stage 23, the synchronous exposure of themask M and the wafer W and the focusing operation of the focusingmechanism 26.

The ΔCD management apparatus 28 will now be discussed with reference toFIGS. 6 and 7. The ΔCD management apparatus 28 measures in what focusstate individual points only in each of measuring shot areasautomatically or manually selected from a plurality of shot areas SAijshown in FIG. 4 (eight areas SA13, SA14, . . . , SA53 and SA54 hatchedin FIG. 4) have actually been exposed. For example, each selectedmeasuring shot area is considered as segments having the slit widths ofthe exposure field 76 and aligned in the scanning direction and the ΔCDmanagement apparatus 28 sequentially measures in what focus state aseries of segment surface portions consecutive at the slit widths in thescanning direction have actually been exposed. Based on the measuringresult, the ΔCD management apparatus 28 analyzes the cause of thevariation amount ΔCD of the exposure line width of a pattern actuallyexposed at each position in each of the measuring shot areas SA13, SA14and so forth, specifically, whether the variation has occurred due tothe focus state at the time of exposure or some other cause.

The ΔCD management apparatus 28 has a CPU 90 which acquires, from thefocusing mechanism 26, pose information (trace data) of the wafer Wwhose area (one of a series of surface portions) including the n-thpoint in individual shot areas SA13, SA14 and so forth has been adjustedby the main control system 27. The CPU 90 stores the pose information ofthe wafer W in a memory 91 as a data storage section in association withpreacquired surface shape information (flatness data) of the exposurearea on the wafer W. The CPU 90 serves as image-state prediction meanswhich predicts the state of the image of a pattern to be transferred onthe wafer W based on the pose information and the surface shapeinformation. The ΔCD management apparatus 28 is constituted by acomputer which comprises an input/output interface circuit section 92,an input section (e.g., a keyboard) 93 and a display section 94 inaddition to the CPU 90 and the memory 91.

At the time a single measuring shot area is scanned with respect to theexposure field 76, the CPU 90 samples the nine focus signals (pre-readdata) output from the signal processor 58 in association with the ninedetection signals from the pre-read sensor L1 or L5 at a predeterminedtiming, e.g., every time the wafer W moves 1 mm in the scanningdirection. The individual pieces of pre-read data (surface positioninformation) obtained from the sampling are sequentially stored in thememory 91.

The CPU 90 also acquires the surface shape information (flatness data)of each measuring shot area during or before scanning exposure. Thedetails of the flatness data will be given later. A flatness-dataacquiring section 95 stores the flatness data in the memory 91 inassociation with the X and Y coordinates of the wafer W. A graphgenerating section 102 generates the flatness data (device topography)of each measuring shot area in the form of a three-dimensional graph asshown in FIG. 12, a contour graph or a numerical table. The displaysection 94 displays the graphs and the like by retrieving.

The CPU 90 acquires, as trace data, the pose of each pre-read area ineach measuring shot area SA13, SA14 or the like which indicates in whatpose the area has been exposed at a position shifted by a predetermineddistance of, for example, 4 mm from the pre-read position. The tracedata is acquired from the sampling data of the aforementioned ninedetection signals at the time of exposure. Specifically, the trace dataincludes Z, pitch and roll control target values that are acquired fromthe nine detection signals pre-read at the pre-read distance of 4 mm andthe amounts of Z, pitch and roll trace errors that are computed byobtaining differences between data pre-read at the pre-read distance of4 mm and saved and real-time data acquired when advanced by 4 mm.Provided that measured values at individual measuring points AF11 toAF59 are denoted by Z11 to Z59, equations for computing the Z, pitch androll control target values and Z, pitch and roll trace errors are givenbelow.

(i) A Z control target value Z_targ is computed from the followingequation 1.

Z_targ=(Z_targ1+Z_targ2+Z_targ3)/3−Pt _(—) cmp  (1)

where

Pt cmp=inclination (device variable) of the wafer table with respect tothe image surface of the projection lens×4 mm.

Z_targ1=average value of used sensors in (Z11, Z21, Z31)

Z_targ2=average value of used sensors in (Z15, Z25, Z35)

Z_targ3=average value of used sensors in (Z19, Z29, Z39)

(ii) A roll control target value R_targ is computed from the followingequation 2.

R_targ=(Z 11+Z 21+Z 31)/3−(Z 19+Z 29+Z 39)/3  (2)

(iii) A pitch control target value P_targ is computed from the followingequation 3.

P_targ=(Z 11+Z 15+Z 19)/3−(Z 31+Z 35+Z 39)/3  (3)

(iv) A Z trace error value Ztrace_err is computed from the followingequation 4.

Ztrace₁₃ err=Z_check2−{(Z_check1)′−(Z_targ)′}  (4)

where

Z_check1 for first checking of Z is

Z_check1=(Z 11+Z 15+Z 19+Z 21+Z 25+Z 29)/6−Pt _(—) cmp 1,

Z_check2 for second checking of Z is

Z_check2=(Z 21+Z 25+Z 29+Z 39+Z 35+Z 31)/6−Pt _(—) cmp 2,

(Z_check1)′ is a computed value of (Z_check1) delayed by (4 mm/scanspeed),

(Z_targ)′ is a computed value of (Z_targ) delayed by (4 mm/scan speed),

Pt_cmp1=inclination (device variable) of the wafer table with respect tothe image surface of the projection lens×6 mm, and

Pt_cmp2=inclination (device variable) of the wafer table with respect tothe image surface of the projection lens×2 mm.

(v) A roll trace error value R_error is computed from the followingequation 5.

R_error=R_check2−{(R_check1)′−(R_targ)′}  (5)

where

R_check1 for first checking of R is

R_check1=(Z 11+Z 21)/2−(Z 19+Z 29)/2,

R_check2 for second checking of R is

R_check2=(Z 21+Z 31)/2−(Z 29+Z 39)/2,

(R_check1)′ is a computed value of (R_check1) delayed by (4 mm/scanspeed), and

(R_targ)′ is a computed value of (R_targ) delayed by (4 mm/scan speed).

(vi) A pitch trace error value P_error is computed from the followingequation 6.

P_error=P_check2−{(P_check1)′−(P_targ)′}  (6)

where

P_check1 for first checking of P is

P_check1=(Z 11+Z 15+Z 19)/3−(Z 21+Z 25+Z 29)/3,

P_check2 for second checking of P is

(P_check1)′ is a computed value of (P_check1) delayed by (4 mm/scanspeed), and

(P_targ)′ is a computed value of (P_targ) delayed by (4 mm/scan speed)

Those pieces of trace data (the Z, pitch and roll control target valuesand Z, pitch and roll trace errors) are sequentially stored in thememory 91 in association with the flatness data.

The graph generating section 102 generates a graph as shown in FIG. 15,which two-dimensionally shows the control target values (targetposition), from the stored trace errors.

The CPU 90 adds the ZT trace (Z, roll and pitch trace errors) to theshot flatness to compute a Z average offset Zave(x1, y, w1, s1) which isan average offset value in the Z direction originated from the traceerrors between the time when an arbitrary point in a shot enters anexposure slit area to tho time when the point leaves that area. In the Zaverage offset, w1 means a wafer number 1 and s1 means a shot number 1.

More specifically, the Z average offset Zave(x1, y) is an average valueof Z-directional trace deviations between the time when a point in theshot (x1, y) enters the exposure slit area to the time when the pointleaves that area, and can be expressed by the following equation 7.$\begin{matrix}{{{Zave}\left( {{x1},y} \right)} = {\sum\limits_{j = {y - n}}^{y + n}\left\lbrack {{Z(j)} + {{{Tx}(j)}*{x1}} + {{{Ty}(j)}*{{am}\left( {y - j} \right)}} - {{{Flt}\left( {{x1},Y} \right)}{I/m}}} \right.}} & (7)\end{matrix}$

where

y is the scan Y coordinate in a shot (when the exposure area has a sizeof 33 [mm], y=0 to 41 [mm] from 33±n [mm]),

m is the number of pieces of data when data is acquired in the slitwidth from the center position of the exposure slit (m=9 with the ypitch=1 [mm]),

n is the number of pieces of data in the slit width on one side(excluding the center position of the exposure slit) (n=(m−1)/2; withthe y pitch=1 [mm], n=4 as m=9),

am is the Y-directional distance from the center position of eachexposure slit in a shot (am(jp)=jp),

Z(j) is the Z target position+Z trace error at a position j in thescanning direction in a shot,

Tx(j) is the roll target position+roll trace error at a position j inthe scanning direction in a shot,

Ty(j) is the pitch target position+pitch trace error at a position j inthe scanning direction in a shot,

Flt(x1, y) is the flatness at coordinates (x1, y) in a shot,

jp, which is a data counter, is jp=−(m−1)/2 to (m−1)/2 (with the ypitch=1 [mm], jp=−4 to 4 as m=9), and

x1 is a coordinate in the exposure slit area.

At the time of measuring the dynamic flatness, the X pitch of an AFsensor used in the measurement is designated. With the X pitch being 2.9[mm], the maximum number of measuring points is nine. At the time ofmeasuring the static flatness, the upper limit of the pitch is normally0.5 [mm] (51 measuring points).

Further, the CPU 90 adds the trace error of the ZT trace (roll, pitchand Z deviations) to the device topography (shot flatness) measured bythe main AF sensor to thereby compute a Z-directional standard deviationZmsd(x1, y) originated from the trace errors between the time when anarbitrary point in a shot enters an exposure slit area to the time whenthe point leaves that area.

More specifically, Zmsd(x1, y) is a Z standard deviation in the exposureslit at a position (x1, y) in a shot and can be expressed by thefollowing equation 8. $\begin{matrix}{{{Zmsd}\left( {{x1},y} \right)} = \sqrt{\begin{matrix}\left\lbrack {\sum\limits_{j = {y - n}}^{y + n}\quad \left\{ {{Z(j)} + {{{Tx}(j)}*{x1}} + {{{Ty}(j)}*{{am}\left( {y - j} \right)}} -} \right.} \right. \\\left. {\left( \left. {{{Flt}\left( {{x1},y} \right)} - {{Zave}\left( {{x1},y} \right)}} \right\} \right)^{2}/m} \right\rbrack\end{matrix}}} & (8)\end{matrix}$

where

Zave(x1, y) is an average value of Z-directional trace deviationsbetween the time when a point in the shot (x1, y) enters the exposureslit area to the time when the point leaves that area,

y is the scan Y coordinate in a shot (when the exposure area has a sizeof 33 [mm], y=0 to 41 [mm] from 33±n [mm]),

m is the number of pieces of data when data is acquired in the slitwidth from the center position of the exposure slit (m=9 with the ypitch=1 [mm]),

n is the number of pieces of data in the slit width on one side(excluding the center position of the exposure slit) (n=(m−1)/2; withthe y pitch=1 [mm], n=4 as m=9),

am is the Y-directional distance from the center position of eachexposure slit in a shot (am(jp)=jp),

Z(j) is the Z target position+Z trace error at a position j in thescanning direction in a shot,

Tx(j) is the roll target position+roll trace error at a position j inthe scanning direction in a shot,

Ty(j) is the pitch target position+pitch trace error at a position j inthe scanning direction in a shot,

Flt(x1, y) is the flatness at coordinates (x1, y) in a shot,

jp, which is a data counter, is jp=−(m−1)/2 to (m−1)/2 (with the ypitch=1 [mm], jp=−4 to 4 as m=9), and

x1 is a coordinate in the exposure slit area.

At the time of measuring the dynamic flatness, the X pitch of an AFsensor used in the measurement is designated. With the X pitch being 2.9[mm], the maximum number of measuring points is nine. At the time ofmeasuring the static flatness, the upper limit of the pitch is normally0.5 [mm] (51 measuring points).

The CPU 90 computes the variation amount ΔCD of the exposure line widthin each measuring shot area from the operation of (prestored designedline width—measured line width) in a line-width-variation computingsection 100. The measured line width is acquired by causing a measuringunit, such as a scanning electron microscope (SEM) to measure theexposure line width of the pattern of each shot area SA13, SA14 or thelike after exposure of all the shot areas on the wafer W is completed.The exposure line width may be measured by using an optical criticaldimension (CD) measurement method, as disclosed in U.S. Pat. No.6,094,256. Wedge mark CD magnification technique uses double exposure asshown schematically in FIG. 19(A). Half the nominal exposure energy isgiven each time. The wedge length is measured using “Laser ScanningAlignment (LSA) sensor” which scans the laser beam spot along the lengthdirection of the wedge and receives the intensity of the scattered lightcoming from it. Designed dimensions are shown in FIG. 19(B) and theirrelationship is expressed in the equation (10). The angle θ is set tosatisfy the equation (11). Thus, the geometric magnification ratio is“50”. Applicants have the comparison between the OCD and SEM measurementresults. The comparison is made after 54 data averaging. The OCD methodreads the wedge length while the SEM observation reads the wedge width.The mutual difference is the order of a few nano meters. $\begin{matrix}{L = {\frac{\left( {{CD1} + {CD2}} \right)}{\sin \quad \theta}{\cos \left( \frac{\theta}{2} \right)}}} & (10)\end{matrix}$

 L=25*(CD 1+CD 2)  (11)

A simple binary distribution of the defocus error can yield almost thesame result as other more complicated defocus distributions. Therefore,Applicants have chosen binary distribution for verification work. If thesimple binary distribution of defocus is realized by exposing twice indifferent focus point, this may require tight alignment accuracy becausethe miss-alignment degrades the CD. If the binary distribution iscombined with wedge mark CD magnification technique, it will requirefour times exposure as well as the tight alignment accuracy control asshown in FIG. 19(B). The CD in first focus point is shown as CD1 and theCD in second focus point is shown as CD2. After taking four timesexposure, the wedge shape is formed and the length of the wedge marl L1becomes measurable.

As one alternative method, Applicants investigated the applicability ofthe staggered focus offset exposure to OCD method. As shown in FIG.19(C), this method requires two exposures in different focus offset toform CD1 and CD2. Due to the self-alignment nature of the wedge mark,there is no alignment error related CD errors. Applicants have doneaerial image simulation to compare the both cases shown FIGS. 19(B) and19(C). The condition of the simulation is as follows; projectedpattern=150 nm isolated line, λ=248 nm, NA=0.68, σ=0.85 conventionalillumination. Mask bias is not introduced. As above mentioned thedifference between them is small, though it can be corrected on contourmap.

The measured line widths of the individual shot areas obtained in theabove manner are entered by the input section 93 and are stored in thememory 91. The graph generating section 102 generates a graph as shownin FIG. 17 three-dimensionally showing the variation amount ΔCD of theexposure line width calculated by the line-width-variation computingsection 100. The variation amount ΔCD may be shown in the form of acontour graph or a numerical table. The graphs of the variation amountΔCD of the exposure line width can be displayed on the display section94 by retrieving.

The operation of the scanning exposure apparatus according to thepresent embodiment will be discussed below.

To begin with, a description will be given of an exposure process forother shot areas SA11, SA12, . . . , SA55 and SA56 than eight measuringshot areas SA13, SA14, SA26, SA21, SA31, SA36, SA53 and SA54 in aplurality of shot areas SAij shown in FIG. 4. The former shot areas willbe simply called “shot areas” in the following description in order todistinguish them from measuring shot areas.

In each shot area, a circuit pattern on a mask M is sequentially exposedwhile synchronously scanning the mask M and the wafer W with respect tothe exposure field 76 as done in the conventional scanning exposureapparatus. Specifically, as shown in FIG. 2, the Y-directional pre-readsensor L1 comprising a plurality of photosensors (which respectivelycorrespond to the measuring points AF11, AF15, AF19, AF21, AF25, AF29,AF31, AF35 and AF39) pre-reads an area 76′ (a pre-read area locatedahead by 4 mm) located in front of the exposure field 76 of a singleshot area in the scanning direction. When this pre-read area is shiftedby a predetermined amount (e.g., 4 mm), the Z-leveling stage 42 is movedto the control target position (roll, pitch and Z-directional height)that is computed based on the pre-read data acquired at the pre-readingtime.

As such pre-reading and the controlled movement of the Z-leveling stage42 are repeated every predetermined time, the circuit pattern is exposedin that shot area. Alternatively, in the exposure process for each shotarea, the control target position of one area may be obtainedimmediately prior to exposure without performing pre-reading and theZ-leveling stage 42 may be moved to that position.

With reference to FIGS. 8 to 10, a description will now be given of theexposure process that is performed on each measuring shot area SA13,SA14 or the like and the ΔCD measuring process that is performed duringthis exposure process.

First, the exposure process that is performed on each measuring shotarea is similar to the exposure process that is performed on each shotarea (SA11, SA12, . . . , SA55 or SA56).

That is, in each measuring shot area, the circuit pattern on the mask Mis sequentially exposed while synchronously scanning the mask M and thewafer W with respect to the exposure field 76.

During this exposure process, a ΔCD measuring process sequence to bediscussed below is executed in each measuring shot area.

(ΔCD Measuring Process Sequence)

(Step 1) Determination of the Shot Map of ΔCD Measuring targets (Step S1in FIG. 8)

Measuring shot areas SA13, SA14 and so forth which are measuring targetsfor ΔCD (variation amount of the exposure line width) are automaticallyor manually designated from a plurality of shot areas shown in FIG. 4.In the case of automatic designation, EGA measuring shot areas orpredetermined exclusive shot areas are selected.

(Step 2) Acquisition of Flatness Data (Step S2 in FIG. 8)

The surface shape information (flatness data) that has a step or thelike of a measuring shot area is acquired during or before exposure. Theflatness data may be acquired by any of the following three ways.

(i) Static Wafer Flatness Measurement (Which Measures the FlatnessBeforehand Using a Wafer Flatness Function)

The flatness of cach shot is measured by the center sensor in theexposure field 76 (the sensor corresponding to the measuring point AF35)using the static wafer flatness function. The measuring pitches in bothX and Y directions can be designated arbitrarily.

(ii) Shot Flatness Measurement in Pre-scan

After auto-focus (AF) in the center of each shot, the shot scan isperformed without AF/AL control and detection values are acquired fromnine sensors (corresponding to the measuring points AF31 to AF39) in thecenter row in the exposure slit. The flatness is measured from thesensor values. It is assumed here that the offset between the sensorshas been compensated previously.

(iii) Shot Flatness Measurement During Exposure

As the maximum number of AF sensors that can read simultaneously iscurrently 3×3=9, the top three sensors (which correspond to AF11, AF15and AF19) are used. Although stage control is not normally performed atthe time of measuring the flatness, the Z-directional height, roll andpitch of each stage are controlled during exposure. To separate theflatness component in a shot, therefore, the stage drive encoder valuesof the Z-directional height, roll and pitch are subtracted from the AFtrace data, as indicated in an equation 9 below.

In the case of the top sensor Sns1 selected for the control purpose, theshot flatness of the row to which Sns1 belongs is acquired from thefollowing equation 9.

Flt _(—) sns_1(x 1, y, w 1, s 1)=Z _(—) aftr(x 1 , y, w 1 , s 1)−Tx _(—)enc(y, z, w 1, s 1)*x 1−Ty _(—) enc(y, w 1, s 1)*y 1−Z _(—) enc(y, w 1,s 1)  (9)

where

(x1, yl) are the coordinates of the sensor from the center of the slit,

Z_attr(x1, y, w1, s1) is the AF trace of the sensor 1 selected for theshot 1 on the wafer 1, and

Z_enc(y, w1, s1), Tx_enc(y, z, w1, s1) and

Ty_enc(y,w1,s1) are encoder traces during exposure on the shot 1 on thewafer 1. It is to be noted that the origin is reset when the first rowof sensors lie over the shot 1.

In the case of the current arrangement of three rows of sensors,Flt_sns_2 (x2, y, w1, s1) and Flt_sns_3 (x3, y, w1, s1) are likewiseacquired. It is also assumed that the offset between the sensors hasbeen compensated previously.

The flatness-data acquiring section 95 stores those pieces of flatnessdata in the memory 91 in association with the X and Y coordinates of thewafer W. The graph generating section 102 generates the flatness data(device topography) of each measuring shot area in the form of athree-dimensional graph as shown in FIG. 12, a contour graph or anumerical table. The display section 94 displays a retrieved one of thegraphs and tile like.

(Step 3) Acquisition of the Measuring Result at Each Measuring Point(Step S3 in FIG. 8)

The CPU 90 acquires, through sampling, focus signals corresponding tothe Z-directional heights of the measuring points AF11, AF15, AF19,AF21, AF25, AF29, AF31, AF35 and AF39 in the pre-read area 76′ of theexposure field 76. This sampling is executed every time the wafer Wmoves by a predetermined distance (e.g., 1 mm)

(Step 4) Computation of Trace Data (Z, Pitch and Roll Control TargetValues and Z, Pitch and Roll Trace Errors) (Step S4 in FIG. 8)

Next, the CPU 90 acquires the Z, pitch and roll control target valueswhen each pre-read area goes to the exposure field and Z, pitch and rolltrace errors (roll, pitch and Z-directional deviation amounts) when thatarea actually reaches the exposure field, one after another inaccordance with sampling. The trace data acquired in this manner isstored in the memory 91 in association with the flatness data, i.e., foreach of the same X and Y coordinates of the wafer W as those of theflatness data. The control target values in the individual measuringshot areas are displayed in the form of a two-dimensional graph as shownin FIG. 15, and the trace errors of the individual portions are alsodisplayed in the form of a two-dimensional graph as shown in FIG. 16.

(Step 5) Computation of Z Average Offset Data (Step S5 in FIG. 8)

The Z average offset is acquired by adding the trace errors computed instep S4 to the flatness data of the individual measuring stol areasacquired in step S2 as described above (see FIG. 10A). As the detailshave already been given earlier, the description will not be repeated.

The Z average offset obtained shows in what pose each portion in eachmeasuring shot area has passed with respect to the exposure field 76.

The Z average offsets of a series of consecutive surface portions(surface portions having the slit width of the exposure field 76) in asingle measuring shot area are acquired one after another in theabove-described manner, and are stored in the memory 91. Those pieces ofthe Z average offset data stored are displayed in the form of athree-dimensional graph as shown in FIG. 13.

(Step 6) Computation of the Movement Standard Deviation (Step S6 in FIG.8)

Next, the CPU 90 causes a movement-standard-deviation computing section99 to calculate, from the equation 2, a standard deviation (movementstandard deviation) Zmsd of a Z-directional trace deviation between thetime when an arbitrary point in the measuring shot area enters theexposure field 76 to the time when the point leaves that field.

The movement standard deviations of a series of consecutive surfaceportions (surface portions having the slit width) in a single measuringshot area are acquired one after another in the above manner, and arestored in the memory 91. The stored movement standard deviations aredisplayed in the form of a three-dimensional graph as shown in FIG. 14.The stored movement standard deviations may be displayed in the form ofa two-dimensional graph or a numerical table.

(Step 7) Determine the Properness of the Exposure Line Width (Step S7 inFIG. 8)

(a) One way to determine the properness of the exposure line width willbe discussed below.

The expected variation amount ΔCD of the exposure line width in eachmeasuring shot area is seen by collating the Z average offsets andmovement standard deviations, both acquired during exposure of theindividual measuring shot areas and stored in the memory 91, with oldstored data during exposure or after exposure of all of the shot areasSAij is completed. When a line-width properness determining section 101decides that the variation amount is equal to or greater than a givenvalue or exceeds a predetermined allowable range, warning can begenerated by displaying a warning indication or the like on the displaysection 94 if it is during exposure. Alternatively, a signal may be sentto the main control system 27 of the scanning exposure apparatus 21 tostop the exposure process. When the value of a variation in line widthactually measured by an SEM or the like after exposure is greater than avariation value originated from the focus error (the focus state at thetime of exposure) that is kept as old data, for example, it isunderstood that the variation in exposure line width has originated fromother causes than the focus error.

(b) The following discusses another way to determine the properness ofthe exposure line width

After exposure of the entire shot areas SAij shown in FIG. 4 iscompleted, the exposure line width of the pattern formed in eachmeasuring shot area is measured using a measuring unit, such as an SEM,and the measured line widths of the individual measuring shot areas areinput to the ΔCD management apparatus 28 through the input section 93.

The line-width-variation computing section 100 computes the variationamount ΔCD of the exposure line width of each measuring shot area fromthe difference between the input measured line width of each measuringshot area and the designed line width of the pattern prestored in thememory 91. The variation amount ΔCD of the exposure line width computedfor each shot area is stored in the memory 91.

When the variation amount of the exposure line width of one measuringshot area is equal to or greater than a given value, the line-widthproperness determining section 101 decides that the variation inexposure line width has originated from other causes than the focuserror and displays a warning or the like on the display section 94.

The variation amount ΔCD of the exposure line widths of the individualmeasuring shot areas are three-dimensionally displayed as shown in FIG.17 by the graph generating section 102. It is seen at a glance from thisgraph how much the exposure line width varies at each portion of eachmeasuring shot area.

The graph shown in FIG. 18 shows the amount of defocus on the horizontalscale and the movement standard deviation Zmsd on the vertical scale andshows the exposure line width in the form of contour lines. The graphshows that for the designed line width of 180 nm, when the defocusamount and the movement standard deviation Zmsd are both small, themeasured value of the exposure line width (measured line width) of eachportion in the measuring shot area actually exposed mostly lies withinthe contour lines of 175 to 180 nm.

Although the value of ΔCD or a variation in line width with respect tothe designed value is calculated and displayed in the embodiment, thevalue of CD or the actual exposure line width may be calculated anddisplayed instead.

A first modification of the first embodiment will be discussed below.The first modification uses correlation data of a defocus and a linewidth value or so-called CD-focus data, instead of the movement standarddeviation Zmsd. The modification can acquire a CD value or ΔCD valuebased on a defocus corresponding to the previously acquired Z averageoffset (FIG. 13) at each point in a Shot and the image height of thatpoint.

The purpose of the modification is to provide a capability of generatinga ΔCD shot map based on the CD-focus data in consideration of theinfluence of the curved image surface of the projection lens. It isassumed that the CD-focus data is prestored as device information.

The ΔCD management apparatus 28 has capabilities of registering, editingand deleting a CD-focus table file and a graph display capability. Atthe time of generating CD-focus data, the defocus amount and CD valueare input in the table for each image height of the projection opticalsystem. The data then can be displayed as shown in FIG. 9. Inconsideration of the influence of the curved image surface of theprojection lens, an approximation is prepared for each image heightbased on the CD-focus data. The approximation may be a linear equation,a quadratic equation or an equation of a higher order.

The number of image heights is determined based on the number of AFsensors in the X direction. At the time of measuring ΔCD, CD is computedfrom the approximation and an average defocus amount (no absolute value)and a ΔCD shot map is generated from the CD.

A second modification of the first amendment will be discussed below. Inthe second modification, the ΔCD management apparatus 28 generates a ΔCD(CD variation) map indicative of sync and dose errors. The FIGS.20(A)-20(D) show introducing the X- and Y-sync errors to a calculationof the CD variation. FIG. 20(A) shows the CD estimation of the sampleshot using CD contour map that is 110 nm isolated line simulationwithout sync error. FIG. 20(B) shows the CD estimation of the same shotas FIG. 20(A). This time as to CD contour map, the one that is the 110nm isolated line simulation with sync error=10 nm in msd value is used.The actual sync error in msd value is not constant. Thus, the sync errordistribution along the scan axis should be known. The snyc errordistribution can be measured on scanner. At this time, the monotonousdistribution as shown in FIG. 20(c) is used. This distribution is madebased on the assumption that the major source of the mechanicaloscillation is the stage acceleration. The amplitude of the oscillationdecrease gradually as the time passes by. Linear interpolation using thesync-error distribution as a weighting function to both CD variationmaps in maximum and minimum sync-errors can give a CD variation map thatrepresent the focus and sync errors as shown in FIG. 20(D). The 3σ andP-P value in CD variation are same as shown in FIG. 20(B). In apractical use, the sync-error and dose-error distributions are veryflat, and their variations or P-P value are very small. Therefore,linear interpolations are applicable.

As shown in FIG. 21, the CD variation map is generated using fourdifferent CD look-up tables that are converted to CD variation maps 301,302, 303 and 304. The variation map 301 has a best sync error in minimumexposure-dose and the variation map 302 has a worst sync error inminimum exposure-dose. The variation map 303 has a best sync error inmaximum exposure-dose and the variation map 304 has a worst sync errorin maximum exposure-dose. A first linear interpolation is performed onthe CD variation maps 301, 302 using a sync error distribution 305 as aweighting function to generate a CD variation map 306 having a syncerror in minimum exposure-dose. A second linear interpolation isperformed on the CD variation maps 303, 304 using a sync errordistribution 305 to generate a CD variation map 307 having a sync errorin maximum exposure-dose. Furthermore, a third linear interpolation isperformed on the CD variation maps 306, 307 using a dose errordistribution 308 along the scan axis that is used as a weightingfunction to generate a CD variation map 309 indicative of sync and doseerrors.

The first embodiment that has the above-described structure has thefollowing advantages.

(1) Using the pose information (trace data) of the wafer W stored in thememory 91 in association with each set of X and Y coordinates at thetime of exposure in what pose the area has been exposed and the surfaceshape information (flatness data) of each measuring shot area on thewafer W, it is possible to see in what pose the surface of the water Wto be exposed has actually been exposed with respect to the exposurefield 76. When the exposure line width of the pattern varies, therefore,it is possible to determine first how much influence the focus error(focus state at the time of exposure) has exerted as a cause of varyingthe exposure line width. This makes it possible to promptly analyze thecause of varying the exposure line width of the pattern.

Specifically, the flatness data shows the surface shape (see FIG. 10A),such as a step of each measuring shot area, and the trace data shows inwhat pose the exposure field 76 has undergone exposure with respect tothe flatness data (see FIG. 10B). Once the two data are known, theamount of deviation (or variation) Zi with respect to the image formingsurface (see FIG. 10C) between the time when the exposure field 76enters and the time when the exposure field 76 leaves, both at eachpoint in the measuring shot area, e.g., point Po shown in FIG. 10B.While each position in each measuring shot area of the exposure surfaceWf is pre-read, the exposure process is carried out by causing theexposure surface Wf to trace the target position. The Z average offsetand the movement standard deviation are however needed as data thatrepresents a pose error indicating in what pose and at what height theslit exposure field 76 passes each point in each measuring shot areaduring the exposure process (see FIG. 11). The Z average offset is theamount of a variation at each point averaged by the slit width of theexposure field 76, and the movement standard deviation is a fluctuationcomponent of the variation at each point, which has been statisticallyprocessed with the slit width. Without the movement standard deviation,one cannot understand whether the amount of fluctuation of the variationvaries significantly or the fluctuation has occurred generally without alarge variation. To know how much each position in each measuring shotarea varies with respect to the image forming surface of the projectionoptical system, therefore, both the Z average offset and movementstandard deviation are needed. In the modification, the Z average offsetand CD-focus data are needed.

(2) If the Z average offsets and movement standard deviations (orCD-focus data) alone are acquired during exposure of the individualmeasuring shot areas or after exposure of all of the shot areas iscompleted, the variation amount of the exposure line width of eachmeasuring shot area can be predicted easily by collating the acquireddata with prestored data of the Z average offset and movement standarddeviation (or CD-focus data) and old data which is comprised of data ofthe exposure line width corresponding to those pieces of data.

(3) A target measuring shot area for which the variation amount ΔCD ofthe exposure line width is to be measured can be selected easilyautomatically or manually from a plurality of shot areas on a map whichshows that shot area.

(4) The Z average offset and movement standard deviation (or CD-focusdata) that are measured during exposure of each measuring shot area canbe registered in a database, e.g., the memory 91 together with variousconditions, such as the then exposure line width, defocus amount,illumination condition (e.g., annular illumination) and the scanningdirection (Y-directional scanning or −Y-directional scanning) at themeasurement. Those registered data can therefore be retrieved as needed.

(5) Based on the trace data and flatness data at the time of exposingeach shot area, the CPU 90 as image-state prediction means can obtainsuch a prediction result that the exposure line width will vary over agiven value during exposure. In the case where such a result isobtained, the ΔCD management apparatus 28 as control means sends themain control system 27 an instruction indicating that exposure isunderway, thereby stopping the exposure process.

(6) The CPU can predict the variation amount of the exposure line widthor the state of the pattern image at the time of exposure, during orafter exposure, by collating the Z average offset and movement standarddeviation obtained during exposure (or preacquired CD-focus data) withold data stored in the memory 91. When the variation amount of theexposure line width actually measured is greater than old data of thevariation amount of the exposure line width stored in the memory 91, itis understood that this variation has originated from other causes thanthe focus error.

(7) Since the variation amount of the exposure line width is displayedon display means, it is possible to easily determine if the displayedvariation amount of the exposure line width exceeds a predeterminedallowable range. For example, the variation amount ΔCD of the exposureline width of each measuring shot area is three-dimensionally displayedas shown in FIG. 17. From the graph, one can see at a glance how muchthe exposure line width varies at each portion in each measuring shotarea. It is therefore possible to easily see the variation amount of theexposure line width with respect to the designed line width.

(8) As shown in FIG. 18, a graph which shows the defocus amount on thehorizontal scale and the movement standard deviation Zmsd on thevertical scale can be prepared. When the defocus amount and the movementstandard deviation Zmsd vary with respect to a given designed linewidth, one can easily see the degree of variation of the measured value(measured line width) of the exposure line width of each portion in ameasuring shot area actually exposed.

(9) As data for displaying various graphs as shown in FIGS. 9 and 12 to18 is saved in the memory 91, data of the necessary graph can beretrieved and displayed on the display section 94. Seeing those graphs,therefore, one can easily manage a variation in the exposure line widthof each measuring shot area for each wafer W.

(10) Because the ΔCD management apparatus 28 is provided as separatefrom the main control system 27 of the scanning exposure apparatus 21and is constituted by a computer, a high-performance scanning exposureapparatus equipped with the ΔCD management apparatus 28 can easily berealized without hardly modifying the conventional scanning exposureapparatus.

(Second Embodiment)

A second embodiment of the scanning exposure apparatus according to thepresent invention will now be described referring to FIGS. 22 and 23.

In the first embodiment, the ΔCD management apparatus 28 is provided asseparate from the main control system 27 of the scanning exposureapparatus 21. In the second embodiment, a ΔCD management apparatus 28Ahaving the equivalent capabilities of the ΔCD management apparatus 28 isincorporated in the main control system 27. The ΔCD management apparatus28A differs from the ΔCD management apparatus 28 only in that it doesnot have the input section 93 and the display section 94. In the secondembodiment, data such as the measured line width can be input through anunillustrated input device provided in the scanning exposure apparatus21. Data of various graphs generated by the ΔCD management apparatus 28Ais stored in a memory 68 as a data storage section in the main controlsystem 27. Therefore, a display device 67 can display graph of thenecessary data by retrieving.

The second embodiment with the above-described structure has thefollowing advantage in addition to the advantages (1) to (10) of thefirst embodiment and modification.

(11) The main control system 27 controls the process of exposing othershot areas than those measuring shot areas hatched in FIG. 4, theprocess of exposing the individual measuring shot areas, and the ΔCDmeasuring process. Unlike the first embodiment, therefore, the secondembodiment does not require a special computer which constitutes the ΔCDmanagement apparatus 28 and can significantly cut the cost downaccordingly.

(Third Embodiment)

A third embodiment of the scanning exposure apparatus according to thepresent invention will now be discussed.

In the third embodiment, the CPU 90 as image-state prediction means hasan image-forming simulation capability (image-forming simulation means)added to the CPU of the first embodiment to calculate the exposure linewidth as the state of the image of a pattern or the variation amount ofthe exposure line width. The CPU 90 of the third embodiment does nottherefore require storage of the data shown in FIG. 18. The thirdembodiment is the same as the first embodiment in other points,

The image-forming simulation capability is to compute the exposure linewidth or the variation amount of the exposure line width based on dataof the Z average offset and movement standard deviation in addition tovarious performances of the projection optical system 24, such as thedesigned line width of a pattern, the defocus amount (the amount of theZ-directional deviation of the exposure surface Wf) and the numericalaperture (NA) of the lens, various kinds of data, such as illuminationcondition (e.g., annular illumination) for illuminating the mask M andthe scanning direction.

The third embodiment calculates the exposure line width or the variationamount of the exposure line width based on data of the Z average offsetand movement standard deviation in addition to various data. Without adatabase where old data of the exposure line widths of patterns isregistered, therefore, the exposure line width or the variation amountof the exposure line width can be predicted during or after exposure ifvarious data is merely input to the CPU 90.

As shown in FIG. 24, a device (a semiconductor chip, such as IC or LSI,a liquid crystal panel, a CCD, a thin-film magnetic head or a micromachine) is manufactured through a step of designing the functions andperformances of the device (e.g., designing the circuit of asemiconductor device) (step 201), a step of producing a reticle (mask)on which a circuit pattern based on the design step is formed (step202), a step of producing a substrate (wafer, glass plate or the like)or the base of the device (step 203), a substrate processing step offorming an actual circuit or the like on the substrate by thelithography technology or the like using the produced or manufacturedreticle (mask) and the substrate (stop 204), a device assembling step ofassembling the device using the processed substrate (including a dicingstep, bonding step and packaging step; step 205) and an inspection stepof performing inspection, such as an operation test for the manufactureddevice and a durability test (step 206).

In the case of a semiconductor device, for example, the wafer processingstep includes an oxidization step of oxidizing the surface of the wafer,a CVD step of forming an insulating film on the wafer surface, anelectrode forming step of forming electrodes on the wafer by vapordeposition and an ion implanting step of implanting ions in the wafer aspre-processing at the individual stages of the wafer process, and isselected and executed in accordance with processes needed at theindividual stages. Post-processing that is executed after thepre-processing is completed includes a resist forming step of coating aphotosensitive material on the wafer, an exposure step of transferringthe circuit pattern on the mask on the wafer using the exposureapparatus and exposure method of each of the above-describedembodiments, a development step of developing the exposed wafer, anetching step of etching off other exposed members than that portionwhere the resist remains, and a resist removing step of removing theresist that has become unnecessary after etching. As thosepre-processing and post-processing are repeated, multiple circuitpatterns are formed on the wafer.

According to the device manufacturing method discussed above, a patternon a reticle is transferred on a wafer by the exposure apparatus andexposure method of each of the above-described embodiments in theexposure step that constitutes the lithography step together with theresist forming step and development step. When the exposure line widthof the pattern varies, therefore, it is possible to determine first howmuch influence the focus state at the time of exposure error has exertedas a cause of varying the exposure line width.

The present invention can also be adapted to an exposure apparatus whichis used in manufacturing a micro device, such as a semiconductor device,a thin-film magnetic head and an image pickup device (CCD or the like).The invention can further be adapted to an exposure apparatus whichtransfers a circuit pattern on a glass substrate or silicon wafer inorder to produce reticles or masks that are used in an optical exposureapparatus, EUV exposure apparatus, X-ray exposure apparatus, electronbeam exposure apparatus and so forth. The exposure apparatuses that useDUV (Deep UltraViolet) rays or VUV (Vacuum UltraViolet) rays generallyuse a transparent type reticle and uses quartz glass, fluorine-dopedquartz glass, fluorite, magnesium fluoride or crystal as a reticlesubstrate. The X-ray exposure apparatus of the proximity type or theelectron beam exposure apparatus uses a transparent mask (stencil maskor membrane mask) and a silicon wafer as a mask substrate.

The exemplified projection optical system and illumination opticalsystem of each embodiment are to be considered as illustrative and notrestrictive. For instance, the projection optical system is not limitedto a refraction optical system, but a reflection system comprising onlya reflection optical element or a reflection refraction system(cata-deoptric system) which has a reflection optical element and arefraction optical element may be used as well. The exposure apparatusthat uses vacuum ultraviolet (VUV) rays having a wavelength of about 200nm or lower may use a reflection refraction system as the projectionoptical system. A reflection refraction system which has a beam splitterand a concave mirror as reflection optical elements, as disclosed in,for example, U.S. Pat. Nos. 5,668,672 and 5,835,275, or a reflectionrefraction system which does not use a beam splitter but uses a concavemirror or the like as a reflection optical element, as disclosed in, forexample, U.S. Pat. No. 5,689,377 and U.S. patent application Ser. No.873,605 (filed on Jun. 12, 1997) can be used as the projection opticalsystem of the reflection refraction type. The disclosures of the U.S.patents and the U.S. patent application are incorporated herein byreference.

The projection optical system may also use a reflection refractionsystem, as disclosed in U.S. Pat. Nos. 5,031,976, 5,488,229 and5,717,518, which has a plurality of refraction optical elements and twomirrors (a main mirror or a concave mirror and a sub mirror or a backmirror which has a reflection surface formed on the opposite side to theincident surface of a refraction element or a parallel plane plate)arranged on the same axis and forms an intermediate image of a reticlepattern, formed by the refraction optical elements, again on a wafer bythe main mirror and sub mirror. In this reflection refraction system,the main mirror and sub mirror are arranged following the refractionoptical elements, and the illumination light passes a part of the mainmirror, is reflected at the sub mirror and the main mirror in the nameorder, and reaches the top of the wafer after passing a part of the submirror. The disclosures of those U.S. patents are incorporated herein byreference.

The projection optical system 24 can use any of a reduction system, anequal magnification system and an enlarging system.

In the first embodiment, when the wafer W is scanned in the Y directionin FIG. 2, the first to third rows of photosensors are used to pre-readan area located ahead of the exposure field 76 on the exposure surfaceWf by 4 mm in the scanning direction. The pre-read area is not limitedto an area located ahead of the exposure field 76 by 4 mm as long as itis located immediately in front of the exposure field 76. Likewise, whenthe wafer W is scanned in the −Y direction in FIG. 2, the fifth to thirdrows of photosensors are used to pre-read an area located ahead of theexposure field 76 on the exposure surface Wf by 4 mm in the scanningdirection. Likewise, the pre-read area is not limited to an area locatedahead of the exposure field 76 by 4 mm as long as it is locatedimmediately in front of the exposure field 76.

Although an area located ahead of the exposure field 76 on the exposuresurface Wf in the scanning direction is pre-read and a target value iscomputed based on the pre-reading result in the first embodiment, theposition of an area on the exposure surface located immediately ahead ofthe exposure field 76 may be measured so that a target value is computedbased on the measured position, and the Z-leveling stage 42 may becontrolled and moved to the target position right after the computationbefore exposure takes place.

The present examples, the embodiments and the modification are to beconsidered as illustrative and not restrictive and the invention is notto be limited to the details given herein, but may be modified withinthe scope and equivalence of the appended claims.

What is claimed is:
 1. A scanning exposure apparatus for projecting animage of a pattern of a mask on a substrate using exposure light andscanning the substrate with the exposure light to expose an exposurearea on the substrate, comprising: surface position detection means fordetecting surface position information of the substrate; adjustmentmeans for adjusting a surface position of the substrate based on aresult of detection by the surface position detection means; and controlmeans for acquiring pose information of the substrate adjusted by theadjustment means at a time of exposure based on a detection signal fromthe surface position detection means and storing the pose information ina memory in association with preacquired surface shape information ofthe exposure area on the substrate.
 2. The scanning exposure apparatusaccording to claim 1, wherein the control means includes image-stateprediction means for predicting a state of the image of the patterntransferred on the substrate based on the pose information and thesurface shape information.
 3. The scanning exposure apparatus accordingto claim 2, wherein the pose information includes a trace error of thesubstrate with respect to a control target position of the substratewhich is adjusted by the adjustment means.
 4. The scanning exposureapparatus according to claim 3, wherein the control means computes atleast one of an average deviation amount of an optical-axial directionalposition of the substrate with respect to a target position at aplurality of measuring points on an exposure surface of the substrateduring irradiation of the exposure light and a standard deviation of afluctuation component of the optical-axial directional position duringirradiation of the exposure light, based on the trace error and thesurface shape information.
 5. The scanning exposure apparatus accordingto claim 4, wherein the control means further includes a data storagesection for prestoriny at least one of the average deviation amount andthe standard deviation of the fluctuation component and data of thestate of the image of the pattern transferred on the substrate inassociation with each other, and the image-state prediction meanspredicts the state of the image of the pattern exposed, based on thestate data of the image of the pattern stored in the data storagesection and at least one of the average deviation amount and thestandard deviation of the fluctuation component which have been acquiredduring exposure or after exposure.
 6. The scanning exposure apparatusaccording to claim 1, wherein the state of the image of the patternincludes line width information of the pattern formed on the substrate.7. The scanning exposure apparatus according to claim 2, wherein theimage-state prediction means includes image-forming simulation means forcomputing the state of the image of the pattern based on data includinga performance of a projection optical system, an illumination conditionfor illuminating the mask and a designed line width of the pattern. 8.The scanning exposure apparatus according to claim 2, further comprisingdecision means for deciding that exposure is abnormal when the state ofthe image of the pattern predicted by the image-state prediction meansgoes off a predetermined allowable range.
 9. The scanning exposureapparatus according to claim 2, further comprising display means fordisplaying the state of the image of the pattern predicted by theimage-state prediction means by at least one of numerical data, atwo-dimensional expression and a three-dimensional expression.
 10. Ascanning exposure method of projecting an image of a mask pattern on asubstrate using exposure light and relatively scanning the substratewith the exposure light to expose an exposure area on the substrate,comprising the steps of: detecting a surface position of the substrateat a time of exposure and detecting pose information of the substrate;and predicting a state of the image of the pattern formed on thesubstrate based on the detected pose information and preacquired surfaceshape information in an exposure area of the substrate.
 11. The scanningexposure method according to claim 10, wherein data of the state of theimage of the pattern transferred on the substrate is prestored inassociation with pose error information acquired from the poseinformation and the surface shape information, and the state of theimage of the pattern formed on the substrate is predicted based on thestored data.
 12. The scanning exposure method according to claim 11,wherein the pose error information includes at least one of an averagedeviation amount of an optical-axial directional position of thesubstrate with respect to a target position at a plurality of measuringpoints on an exposure surface of the substrate during irradiation of theexposure light and a standard deviation of a fluctuation component ofthe optical-axial directional position during irradiation of theexposure light.
 13. The scanning exposure method according to claim 10,wherein the state of the image of the pattern includes line widthinformation of the pattern formed on the substrate.
 14. The scanningexposure method according to claim 10, further comprising the step ofdeciding that exposure is abnormal when the predicted state of the imageof the pattern goes off a predetermined allowable range.
 15. Amanagement apparatus for managing exposure process information of ascanning exposure apparatus which includes surface position detectionmeans for detecting surface position information of a substrate andadjustment means for adjusting a surface position of the substrate basedon a result of detection by the surface position detection means, thescanning exposure apparatus projecting an image of a pattern of a maskon the substrate using exposure light and scanning the substrate withthe exposure light to expose an exposure area on the substrate, themanagement apparatus comprising: an interface connected to the scanningexposure apparatus; and control means for acquiring pose information ofthe substrate adjusted by the adjustment means at a time of exposurebased on a detection signal from the surface position detection meansacquired via the interface, and storing the pose information in a memoryin association with preacquired surface shape information of theexposure area on the substrate.
 16. The management apparatus accordingto claim 15, wherein the control means includes image-state predictionmeans for predicting a state of the image of the pattern transferred onthe substrate based on the pose information and the surface shapeinformation.
 17. The management apparatus according to claim 16, whereindata of the state of the image of the pattern transferred on thesubstrate is prestored in association with pose error informationacquired from the pose information and the surface shape information,and the image-state prediction means predicts the state of the image ofthe pattern formed on the substrate based on the stored data.
 18. Themanagement apparatus according to claim 17, wherein the pose errorinformation includes at least one of an average deviation amount of anoptical-axial directional position of the substrate with respect to atarget position at a plurality of measuring points on an exposuresurface of the substrate during irradiation of the exposure light and astandard deviation of a fluctuation component of the optical-axialdirectional position during irradiation of the exposure light.
 19. Themanagement apparatus according to claim 16, wherein the state of theimage of the pattern includes line width information of the patternformed on the substrate.
 20. The management apparatus according to claim16, further comprising decision means for deciding that exposure isabnormal when the predicted state of the image of the pattern goes off apredetermined allowable range.
 21. A management method of managingexposure process information of a scanning exposure apparatus whichincludes surface position detection means for detecting surface positioninformation of a substrate and adjustment means for adjusting a surfaceposition of the substrate based on a result of detection by the surfaceposition detection means, the scanning exposure apparatus projecting animage of a pattern of a mask on the substrate using exposure light andscans the substrate with the exposure light to expose an exposure areaon the substrate, the management method comprising the steps of:acquiring a detection signal of the surface position detection means viaan interface from the scanning exposure apparatus; acquiring poseinformation of the substrate adjusted by the adjustment means at a timeof exposure; and predicting a state of the image of the pattern formedon the substrate based on the pose information and preacquired surfaceshape information of the exposure area on the substrate.
 22. Themanagement method according to claim 21, wherein data on the state ofthe image of the pattern transferred on the substrate is prestored inassociation with pose error information acquired from the poseinformation and the surface shape information, and the state of theimage of the pattern formed on the substrate is predicted based on thestored data.
 23. The management method according to claim 22, whereinthe pose error information includes at least one of an average deviationamount of an optical-axial directional position of the substrate withrespect to a target position at a plurality of measuring points on anexposure surface of the substrate during irradiation of the exposurelight and a standard deviation of a fluctuation component of theoptical-axial directional position during irradiation of the exposurelight.
 24. The management method according to claim 21, wherein thestate of the image of the pattern includes line width information of thepattern formed on the substrate.
 25. The management method according toclaim 21, further comprising the step of deciding that exposure isabnormal when the predicted state of the image of the pattern goes off apredetermined allowable range.
 26. A device manufacturing methodcomprising the step of: executing a lithography process using a scanningexposure method of projecting an image of a mask pattern on a substrateusing exposure light and relatively scanning the substrate with theexposure light to expose an exposure area on the substrate, the scanningexposure method including the steps of: detecting pose information ofthe substrate by detecting a surface position of the substrate at a timeof exposure; and predicting a state of the image of the pattern formedon the substrate based on the detected pose information and preacquiredsurface shape information in an exposure area of the substrate.
 27. Adevice manufacturing method comprising the step of: executing alithography process using a management method of managing exposureprocess information of a scanning exposure apparatus which includessurface position detection means for detecting surface positioninformation of a substrate and adjustment means for adjusting a surfaceposition of the substrate based on a result of detection by the surfaceposition detection means, the scanning exposure apparatus projecting animage of a pattern of a mask on the substrate using exposure light andscanning the substrate with the exposure light to expose an exposurearea on the substrate, the management method including the steps of:acquiring a detection signal of the surface position detection means viaan interface from the scanning exposure apparatus; acquiring poseinformation of the substrate adjusted by the adjustment means at a timeof exposure; and predicting a state of the image of the pattern formedon the substrate based on the pose information and preacquired surfaceshape information of the exposure area on the substrate.